The present invention relates to rotary fluid pressure devices, and more particularly, to lubrication circuits for such devices.
Although it should become apparent from the subsequent description of the invention that it may be useful with many types of rotary fluid pressure devices, including both pumps and motors, it is especially advantageous when used in a fluid motor and will be described in connection therewith.
Also, although the invention may be used with devices having various types of internal gear sets, the invention is especially adapted for use in a device including a gerotor gear set, and will described in connection therewith.
Fluid motors of the type utilizing a gerotor gear set to convert fluid pressure into a rotary output have become popular and are especially suited for low speed, high torque applications. In one of the most common designs of such motors, the housing defines inlet and outlet ports and a cylindrical valve bore, and the motor includes a hollow, cylindrical spool valve which is integral with the output shaft. The well known commutating valve action necessary to communicate pressurized fluid to the expanding volume chambers of the gerotor set and communicate exhaust fluid from the contracting volume chambers occurs at the interface of the housing bore and valve spool.
Thus, in a motor of the type described, there are three different pressure "zones":
1. the high pressure zone extending from the inlet port to the expanding volume chambers;
2. the low pressure zone extending from the contracting volume chambers to the outlet port; and
3. the case drain zone (lubrication fluid chamber).
The lubrication fluid chamber is typically the central region of the motor defined by the hollow spool valve, the externally toothed gerotor star, and the housing. A major portion of the fluid entering this chamber is leakage fluid from the pressurized gerotor volume chambers. In addition, a certain amount of leakage fluid flows through the cylindrical clearance between the spool valve and housing bore and enters the lubrication chamber at either the forward end, or the rearward end, depending upon the direction of operation of the motor.
In most of the commercially available motors of the type described above, output torque is transmitted from the externally toothed member of the gerotor set to the output shaft assembly by means of a dogbone shaft which is in splined engagement with both the externally toothed gerotor member and the output shaft. One of the primary factors limiting the torque output capability of such motors is the strength of these two spline connections. It has long been recognized by those skilled in the art that the strength of these spline connections may be increased by improving lubrication flow through the spline connections. Therefore, the primary function of leakage fluid which enters the lubrication chamber is to flow through the spline connections to prevent metal to metal contact of the splines, and to remove heat and contamination particles.
In one of the typical prior art devices, lubrication fluid was forced to flow through a very restricted flow path, even after passing through the spline connections, with the rsult that contamination particles could become trapped between relatively movable portions of the motor, rather than being flushed out of the motor.
In another prior art design, the motor was provided with an external case drain connection to permit relatively unrestricted flow of lubrication fluid. In one direction of motor operation, the result would be good lubricant flow through both splines connections, but in the opposite motor direction, the result would be lubricant flow through one of the spline connections (typically the spline connection with the gerotor), but negligible lubricant flow through the other spline connection.